The Science of Resistance Training
The health benefits associated with resistance training are not under debate and include decreased gastrointestinal transit time, reduced risk of colon cancer, increased resting metabolic rate, improved glucose metabolism, improved blood-lipid profiles, reduced resting blood pressure, improved bone mineral density, pain, and discomfort reduction for those suffering from arthritis, decreased lower back pain, enhanced flexibility, and improved aerobic capacity. What has been under debate is how to do it best. 1 The American College of Sports Medicine, long considered the expert in resistance training, has dispensed poor advice over the years, largely unsupported by rigorous science.
In 2011, researchers used existing studies that employed rigorous science to more fully understand how we should work out. They included intensity, the number of repetitions, the length of training sessions, the volume of work, whether core exercises are as important as we think, the speed of repetitions, rest time between sets, and whether free weights are better than machines. Their findings might surprise you.
Intensity
Commonly, the percentage of your one rep maximum has been the standard intensity measurement. However, the researchers found this measurement to be lacking. They postulated that intensity is the maximum reps possible before muscular failure for any given weight. Following this postulate to its conclusion, they conclude that when you can no longer lift the weight, you have reached 100% maximum intensity. They called this momentary muscular failure. Based on their findings, rather than performing multiple sets, the same muscular strength and endurance adaptations can be attained by performing a single set of around 8-12 repetitions to momentary muscular failure. Amazingly, the research evidence does not support the view that training with a relatively high percentage of your one rep maximum is important for strength development. 1 In other words, heavier is not better. The assumption that load x repetitions = intensity is a fallacy.
Number of repetitions
In 2002, Folland et al. found that training to failure could save workout time. They tested routines of 25 minutes, compared to 7 minutes with muscle failure, and found no difference in the outcome. Studies do not support the hypothesis that higher repetition workouts are more effective in increasing muscular endurance. Anderson and Kearney found that the number of reps did not affect strength outcome. Stone and Coulter found the same. Lastly, since we understand that one set to muscular failure is key, additional sets where muscular failure does not happen only add effort and time, not results.
Length of Training Sessions
We already know that one set to complete muscular failure achieves the same result as multiple sets without failure, so it stands to reason that the length of time spent training does not correlate to more gains.
Volume of Work
The number of times we work out increases the volume of work. Carpinelli et al. and Smith and Bruce-Low reviewed multiple studies and concluded that there is little or no difference between training 1, 2, or 3 times per week. Once again, a single set performed to momentary muscular failure can produce the same gains as multiple sets in muscle function. Training most major muscle groups once or twice weekly is sufficient to attain strength gains equal to training at a greater frequency. 1
Core Strengthening
Everyone has heard about the wisdom of strengthening our core. The core muscles stabilize our limbs. Kibler, Press, and Sciascia define the core as proximal stability for distal mobility. A strong core provides a foundation for movement and forces the arms and legs generate. A strong core helps with sports and day-to-day activities and can help prevent injury. I caution that you don't work your core by working on an unstable platform. The research shows no benefits, and the risk of injury due to instability is increased. You should isolate one side. When you do this, your core must stabilize to perform unilateral limb movements against resistance. 1
Speed of Repetitions
A comprehensive review of studies on faster lifting speeds during resistance training revealed no benefits. Bruce-Lowand Smith revealed that explosive exercises like Olympic lifting increased the risk of injuries to multiple body areas and do not produce any benefits for strength and hypertrophy. Therefore, the duration that maintains muscular tension throughout the entire range of motion is preferential.
Rest Time Between Sets
A 2012 review of 35 studies examined resistance training outcomes with rest interval length as the experimental variable. When the training goal is muscular hypertrophy, the combination of moderate-intensity sets with shorter rest intervals of 30–60 seconds might be most effective due to greater acute growth hormone levels generated during these workouts. In 2014 researchers found that high-intensity strength resistance training with shortened rest intervals between sets resulted in significantly greater enhancements in body composition, muscular performance, and functional performance compared to longer rest intervals in older men. 1 Finally, in 2021, researchers demonstrated that shorter rest intervals between sets lead to increases in circulating testosterone which explains the increase in size and strength associated with shorter rest intervals. 2
Free Weights Versus Machines
The evidence does not support the superiority of one particular form of resistance for gaining muscle strength, power, or endurance. The choice of equipment should be dictated by personal preference, convenience, and risk of injury. However, machines are less likely to cause injury than free weights.
My Experience
I found out decades ago that lifting heavy weights close to my one rep max was a mistake. When I was younger, I thought I had to continually push the poundage for progress. The stresses and strains were too much to handle, and I was constantly injured and forced to take time off. Of course, I now know I would have had more gains with shorter workouts and working to failure with lighter weights.
Now I lift just enough to get to momentary muscular failure in a brief time. I do vary between (so-called) heavy and light days, but the weight is insignificant. One day I will do sets of 20 reps using lighter weights; another day, I will go with heavier weights and only do sets of 4 reps to failure. I never miss time in the gym due to an injury. I prefer machines over free weights because I find I don’t get injuries as easily using them. I recently added a Bioforce machine ($300, used) that uses a pneumatic piston system, and I really like it. Since it has no weight, there is no inertia while moving, which helps my form, further decreasing my odds of injury.
Genetics
There are many more factors to strength and size, like sleep and diet. The largest factor is genetics. Some people can add muscle and strength easily, while others are hard gainers. Don’t be fooled by fitness gurus pushing their own brand of supplements and workout plans, thinking they will make you look like them. Chances are you won’t. If you are looking fortraining advice, Nate Miyaki is trustworthy.